NCERT Solutions for Class 10 Science Chapter 8 How Do Organisms Reproduce

NCERT Intext Questions

 Page Number 128

1. What is the importance of DNA copying in reproduction?

Ans. Importance of DNA copying in reproduction is as follows:

  1. It helps in transferring characters from parents to offspring.
  2. It is helpful in continuity of species.
  3. When DNA is copied some variation is present.
  4. DNA is produced from sexual reproduction so different parents are involves, it leads evolution of new species.

2. Why is variation beneficial to the species but not necessarily for the individual?

Ans. Variations are beneficial to the species than an individual because sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult. During that period only few variants that are resistant would be able to survive. Thus variant helps in survival of species. However all variations are not necessarily beneficial for the individual organism.

 Page Number 133

1. How does binary fission differ from multiple fission?

Ans.

Binary fission Multiple fission
1. Parent cell divides itself into two equal and identical daughter cells. A single parent cell divides into many daughter cells.
2. In binary fission, division occurs one time. In multiple fission, division occurs repeatedly.
3. In this, both cytoplasm and nucleus divide simultaneously. In this, nucleus divides first.
4. It generally occurs in favourable conditions Example : Amoeba, paramecium. It can take place in unfavourable conditions too. Example: Malarial parasite, plasmodium.

2. How will an organism be benefited if it reproduces through spores?

Ans. An organism will be benefited if it reproduces through spores because:

  1. It is simpler and faster mode of asexual reproduction.
  2. Spores are very small and light in weight so can disperse easily through water, wind and animals etc.
  3. Spore is having thick layer around it which protects it in unfavourable conditions. When favourable condition occurs, it will
    grow again. 

3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

Ans. Higher complex animals cannot give rise to new individuals through regeneration because complex organisms have organs system level of organization, where all organs work together as an interconnected unit. They can regenerate their lost body parts such as skin, muscles, blood etc. However they could not give rise to new individuals through regeneration.

4. Why is vegetative propagation practised for growing some types of plants?

Ans. Vegetative propagation is practiced for growing some types of plants because of following reasons:

It is very easy and fast rpocess.

It can help to grow the plants in such region where germination failed.

It is useful for the propagation of those plants that do not produce viable seeds or whose seeds production in very less in number.

5. Why is DNA copying an essential part of the process of reproduction?

Ans. DNA is a hereditary material, which passes from one generation to another generation or from parents to offsprings. DNA contains genetic information which has codes for the protein synthesis through translation. The changes in the copy of DNA make an organism capable to survive in changing conditions.

 Page Number 140

1. How is the process of pollination different from fertilisation ?

Pollination Fertilisation
1. The transfer of pollen grains from the anther of a stamen to the stigma of a carpel is called pollination. Fertilisation occurs when the male gamete present in pollen grain joins with the female gamete (or egg) present in ovule.
2. It is an exterior process that occurs on the outside of a flower. It is an internal process that occurs within an flower.
3. It takes place by various pollinating agents. It takes place by natural or artificial means.
4. Only flowered plants are pollinated. It occurs in both plants as well as animals.

2. What is the role of the seminal vesicles and the prostate gland?

Ans. Prostate gland secretes prostate fluid, which is a component of semen, which protects the sperm from acidic environment in female vaginal tract. Seminal vesicles secrete a significant proportion of fluid that ultimately becomes serum when mixed with sperm.

3. What are the changes seen in girls at the time of puberty?

Ans. At the time of puberty secondary sexual characters develop:

  1. Voice becomes thin.
  2. Menstruation beings.
  3. Mammary glands develop and enlarge.
  4. Fallopian tube, uterus and vagina enlarge.
  5. Eggs start releasing from ovaries.

4. How does the embryo get nourishment inside the mother’s body?

Ans. Embryo gets nourished inside the mother’s body by a special structure called placenta. It transports materials such as glucose, oxygen etc. from mother to embryo.

5. A woman is using a copper-T. Will it help in protecting her from sexually transmitted diseases?

Ans. Copper-T is a contraceptive method which prevents implantation of the zygote inside the uterus. It cannot prevent a women from sexually transmitted diseases. These diseases are transmitted by contact which cannot be prevented by copper-T. It can only prevent pregnancy.

NCERT Exercise Questions

1. Asexual reproduction takes place through budding in:

  • (a) Amoeba.
  • (b) Yeast
  • (c) Plasmodium
  • (d) Leishmania
  • Ans. (b) Yeast
  • Explanation: Amoeba and Leishmania reproduce through binary fusion, plasmodium through multiple fission and yeast through budding.

2. Which of the following is not a part of the female reproductive system in human beings?

  • (a) Ovary
  • (b) Uterus
  • (c) Vas deferens
  • (d) Fallopian tube
  • Ans. (c) Vas deferens
  • Explanation: Vas deferens is a part of male reproductive system whereas ovary, uterus and fallopian tube are the part of female reproductive system.

3. The anther contains:

  • (a) Sepals
  • (b) Uterus
  • (c) Carpel
  • (d) Pollen grains
  • Ans.(d) Pollen grains
  • Explanation: The outer contains male gamete called pollen grains.

4. What are the advantages of sexual reproduction over asexual reproduction?

Ans. Advantages of sexual reproduction over asexual reproduction:

  1. In asexual reproduction the offspring are almost identical to their parents because they have same gene as their parents so in this variations are very few. In sexual reproduction offspring is similar to parents but not identical to them, because of mixing of genes from mother and father. This leads to greater variety in population.
  2. In asexual reproduction only few variations have little evolutionary importance. Sexual reproduction promotes diversity of characters in offsprings by providing genetic variations which lead to evolution of species.
  3. Offspring produced by asexual reproduction are unable to adopt to the changing environment. Offspring produced by sexual reproduction has better adaptability to the changing environment.

Thus sexual reproduction have advantages over asexual reproduction in terms of variations, evolution and adaptability.

5. What are the functions performed by the testis in human beings?

Ans. There are two major functions of testes-one is to secrete hormone called testosterone, responsible for development of secondary sexual characters and others to produce male gametes, called sperms.

6. Why does menstruation occur?

Ans. Menstruation occurs due to the rupture or removal of the inner, thick and soft lining of uterus when fertilization does not take place. So, the thick and soft inner lining of uterus along with the blood vessels and dead ovum comes out in the form of blood, called menstruation.

7. Draw a labelled diagram of the longitudinal section of a flower.

Ans.

How Do Organisms Reproduceans7

8. What are the different methods of contraception?

Ans. The different methods of contraception are as follow:

  1. Barrier method: In this method, condom, diaphragm and cervical caps are used. These prevent the entry of sperms in the female genital tract during sexual intercourse.
  2. Chemical method: In this method a woman uses two kinds of pills (oral and vaginal pills). The oral pills are hormonal preparations which suppress the release of ovum in fallopian tube. These are called oral contraceptives. The vaginal pills/creams are spermicidal. The chemicals in these spermicidals kill the sperms during their journey in the vaginal tract.
  3. Intrauterine contraceptive devices: Intrauterine contraceptive devices such as copper-T are placed safely in the uterus by a skilled doctor. It prevents the sperms to reach the uterus.
  4. Surgical method: In this method, a small part of vas deferens of male and fallopian tube of female is cut or tied by surgery. It is called vasectomy in males and tubectomy in females.

9. How are the modes for reproduction different in unicellular and multicellular organisms?

Ans.

Pollination Fertilisation
1. Asexual reproduction takes place in unicellular organisms by means of binary fission, budding, fragmentation etc. Multicellular organisms can divide by sexual as well as asexual method. Vegetative propagation in plant is means of asexual reproduction.
2. Only one parent is required in this method to produce identical offspring. A male and a female both are required in this method. The offsprings are similar to parents but not identical.
3. It does not involve the fusion of gametes. Fusion of male and female gametes is involved.
4. No special cells and organs are present for reproduction. Special cells and organs are present for reproduction located at the fixed position in the body.

10. How does reproduction help in providing stability to populations of species?

Ans. Reproduction is the process by which organisms give rise to offspring of the same species. Since every individual grows old and ultimately dies, new individuals of same species are needed to be produced. Therefore reproduction is important to maintain the species and provide stability.

11. What could be the reasons for adopting contraceptive methods ?

Ans. The reasons for adopting contraceptive devices are:

  1. To prevent unwanted pregnancies.
  2. To prevent the transfer of sexually transmitted diseases.
  3. To control birth rate and prevent population rise.